The present invention relates to a linear motion drive, in particular for generating a linear motion from a rotary motion while permitting independent manual linear operation.
There are many uses for linear motion drive devices. For instance, linear motion drive devices is particular suitable for locking or unlocking a door locking mechanism or the like. Power door locks, for example, have been in use for locking and unlocking doors in automobiles. There are many different types of actuators for actuating a locking mechanism for doors or the like.
A typical power lock mechanism comprises an electrical motor, and a rotary-to-linear transmission mechanism which translates rotary motion from the motor to a linear motion for actuating a door locking mechanism. The rotary-to-linear mechanism typically includes a reversibly rotatable lead-screw and a carriage which linearly rides in the longitudinal direction of the lead-screw as the lead-screw rotates or a rack and pinion type where the motor drives a pinion (gear) and causes the rack (carriage) to move linearly. The carriage or rack is mechanically connected to the locking mechanism.
If the lead-screw/carriage or rack and pinion is directly linked to the locking mechanism, manual operation may be hindered or rendered difficult since the motor has to be back driven. U.S. Pat. No. 4,723,454 issued to Periou et al, for instance, uses a carriage which slides along the lead-screw to permit manual operation. In particular, the lead-screw is permitted to freely rotate in both directions when the motor is not energized. The carriage is integral with a locking mechanism attaching end. By manually pushing or pulling the attaching end, the carriage can be moved linearly relative to the lead-screw. A drawback of this type is that manual operation causes back driving of the lead-screw and the motor, which increases the manual force necessary to operate the locking mechanism. Moreover, because the carriage actually rides on the helical groove of the lead-screw, the carriage does not readily move in the linear direction.
Many different devices have been contemplated in the past to prevent back driving of the motor and the lead-screws or the like during manual operation. U.S. patents U.S. Pat. No. 4,290,634 issued to Gelhard; U.S. Pat. No. 4,821,521 to Schuler; U.S. Pat. No. 4,893,704 to Fry et al; U.S. Pat. No. 4,978,155 to Kobayashi, for instance, show various types of devices for preventing back driving of the motor during manual operation.
U.S. Pat. No. 4,978,155 uses a clutch mechanism between a drive shaft and an output shaft to transmit power from the drive shaft to the output shaft. Specifically, the drive shaft is directly connected to the output of the motor and the output shaft is connected to a lock mechanism operating rod. The operating rod moves linearly about the longitudinal axis of the output shaft via a helical thread formed on the output shaft. The clutch mechanism couples the drive shaft to the output shaft only when the motor is energized. At all other times, the output shaft freely rotates relative to the drive shaft. Similar to U.S. Pat. No. 4,723,454, the operating rod may be manually depressed or extended, but such action causes the output shaft to rotate during manual operation, which increases the force necessary to move the operating rod. However, due to the clutch mechanism, the motor is not back driven in this type of arrangement.
U.S. Pat. No. 4,893,704, on the other hand, uses complicated, coaxially arranged inner main and outer secondary shafts having opposed external threads that cooperate to send a drive member to a neutral position without changing the direction of the motor during manual operation. Specifically, the drive member is connected to the outer secondary shaft via a lost motion device to permit manual operation without back driving the motor. However, a drawback with this type of device is that the shaft needs to be further driven after the locking mechanism has been already actuated to position the drive member in a neutral position.
U.S. Pat. No. 4,290,634 shows a use of a flywheel that is connected to a motor to store energy which is used to actuate the door lock mechanism. When the lock operation is completed, the flywheel is uncoupled from the lock so that its residual energy is not absorbed by the lock to permit manual operation without turning the flywheel during manual operation. Specifically, one end of the rack has an abutment head which may be shifted into engagement with a C-shaped connector, which is connected to the lock mechanism and a manual operating knob, by suitably turning the pinion to drive the rack. A spiral spring is operatively connected to a shaft of the pinion to rotate the pinion using the energy stored in the spring to bring the abutment head in a neutral position to permit the manual knob to be depressed or extended without interference from the abutment head. In other words, a lost-motion type of connector is provided between the abutment head and the lock mechanism via the C-connector.
U.S. Pat. No. 4,821,521, similar to U.S. Pat. No. 4,290,634, uses the energy stored in a coil or helical spring to bring the positioning element, which is connected to a locking mechanism, to an initial position when the motor is shut off. In this device, the positioning element is threadingly engaged with the gear spindle. The positioning element appears to be brought back to whatever position it was in prior to the actuation of the motor. It appears that there can be no manual operation with this type of actuator, or, at the very least, manual operation will be rather difficult since the positioning element is threadingly engaged to the gear spindle. Any type of manual operation disadvantageously requires the spindle and thus the motor to be back driven.